The use of weigh-in-motion weighing devices to weigh moving objects should be quite familiar to one of skill in the art. Such weigh-in-motion devices are also commonly referred to as checkweighers. While various particular checkweigher designs exist, a typical in-line checkweigher (hereinafter just “checkweigher” for brevity) may be described generally as a weighing device designed to weigh objects as the objects travel—often at relatively high speed—along a conveyor. Consequently, a checkweigher is typically installed in a conveyor line between an infeed conveyor that delivers objects to the checkweigher and a discharge conveyor that transports weighed objects from the checkweigher to a downstream location.
Typically, checkweighers are used to determine whether objects being weighed are of an expected weight or within some acceptable range or zone around an expected weight. If the weight of an object is deemed acceptable by a checkweigher, the object is normally passed to a downstream location, where the object may be further processed, packaged, etc. If the weight of an object is deemed unacceptable by a checkweigher, the object may be rejected. An objective of such a checkweigher is not only to reject objects of improper weight, but also to minimize the occurrence of false rejections.
Very broadly speaking, a typical checkweigher of the aforementioned type includes a scale, which is essentially a vertically deflectable mechanism having a weigh platform and being operable to effect weighing of the moving objects through the use of load cells or other force detecting elements in combination with associated electronics, software, etc. Such a checkweigher also typically employs its own conveyor to transport objects received from the infeed conveyor across the scale and to the discharge conveyor.
The weight of a given object is normally determined through the continuous collection of weight data from the scale (i.e., the weigh-signal), which begins to accumulate when the weight of the object is fully supported by the scale and continues as the object moves across the scale. This weight data is then processed (e.g., filtered, averaged, etc.) to produce a single weight value that is associated with the object. While checkweighing has been known and used for some time, there are nonetheless deficiencies inherent to known checkweighing systems and methods that would be advantageous to overcome.
In order to provide accurate weight readings, it must be must ensured that only a single object to be weighed is in contact with the scale during the weighing data collection process. Similarly, because the weight of an object to be weighed must be fully supported by the scale, no portion of the object may be supported by the infeed or discharge conveyors during a weighing operation.
Any noise that is introduced into the collected weight data during the weighing process can also negatively affect the accuracy of object weight readings. One source of such noise is mechanical vibration of the scale that frequently occurs as an object transitions from the infeed conveyor onto the weigh platform of the checkweigher scale. Because such noise is reduced as the object settles, it is currently common practice to utilize a weigh platform that is longer than an object being weighed. The additional weigh platform length allows the object sufficient time to settle, resulting in object weight data with less inherent noise and improved accuracy.
It should be understood that optimal weighing is achieved when signal noise is minimized, and when weigh time is maximized to allow for greater weight data collection. Unfortunately, because modern processing operations place a premium on throughput, checkweigher users desire to minimize, not maximize, weigh time. As a result, weighing accuracy is often sacrificed for increased weighing speed.
Known checkweighers also utilize photo-sensors to determine when objects transition on and off the weigh platform. A weight data processing algorithm uses signals from these photo-sensors to determine which portions of the incoming weight data stream to analyze. Current weighing algorithms require that weight data processing be performed when the object being weighed reaches an evaluation point, i.e., a fixed position on the scale (e.g., 97% of the scale length). Once the object reaches the evaluation point it is assumed that noise is minimal and an acceptable amount of weight signal data has been collected. If a subsequent (upstream) object makes contact with the scale before the object being weighed reaches the evaluation point, known processing algorithms discard all collected weight signal data based on the assumption that the level of noise and amount of weight signal data is unacceptable for making an accurate object weight determination. This commonly leads to an object being unnecessarily rejected—not because the weight of the object is actually unacceptable, but because the weight of the object could not be adequately determined.
An upstream-located gapping belt conveyor may be used to pull gaps between incoming objects to assure a good read and sort prior to being put through label applicators or printers, barcode scanners, checkweighers and sorters by accelerating or decelerating of the gapping belt conveyor. The same situation of unnecessarily rejected objects could result if the clearance of the objects is too short due to a spacing fault established at the gapping belt conveyor.